sim: add stubs for new API

Not really functional - but this is a really signficant speed boost
for actual device firmware.

sim/fakes/_sim.py

@@ -474,6 +474,11 @@ def get_ctx():
     return ctx.Context(dctx)
 
 
+def get_overlay_ctx():
+    dctx = ctx._wasm.ctx_new_drawlist(240, 240)
+    return ctx.Context(dctx)
+
+
 def display_update(subctx):
     _sim.process_events()
     fbp, c = fbm.get()

sim/fakes/ctx.py

@@ -100,6 +100,7 @@ class Context:
     LEFT = "left"
     RIGHT = "right"
     CENTER = "center"
+    CLEAR = "clear"
     END = "end"
     MIDDLE = "middle"
     BEVEL = "bevel"

sim/fakes/sys_display.py

@@ -5,5 +5,10 @@ def pipe_full():
     return False
 
 
+def set_overlay_height(foo):
+    pass
+
+
 update = _sim.display_update
 get_ctx = _sim.get_ctx
+get_overlay_ctx = _sim.get_overlay_ctx